Liquid Crystal Displays (LCDs) are widely used flat panel display devices. As is well known to those having skill in the art, an LCD generally includes two spaced apart substrates with liquid crystals therebetween. A plurality of spaced apart gate lines are formed on one substrate, and a plurality of spaced apart data lines are formed on the substrate that intersect the plurality of spaced apart gate lines. Accordingly, the gate lines and data lines define an array of pixels. An array of pixel electrodes is provided, a respective one of which is in a respective one of the pixels. An array of thin film transistors is also provided, each comprising a gate electrode that is connected to one of the spaced apart gate lines, a gate insulator on the gate electrode, and an amorphous silicon layer on the gate insulator. Spaced apart source and drain electrodes are provided on the amorphous silicon layer. The source electrode is connected to one of the spaced apart data lines. The drain electrode overlaps a pixel electrode, and is electrically connected thereto through a contact hole therebetween.
As is well known to those having skill in the art, the thin film transistors generally include an undoped hydrogenated amorphous silicon layer that forms the channel region. A doped hydrogenated amorphous silicon layer that may be heavily doped, for example, with n-type impurities, is formed on the undoped amorphous silicon layer. The doped amorphous silicon layer can decrease the contact resistance between the amorphous silicon layer and source/drain electrodes. The doped amorphous silicon layer is then selectively etched using patterned source/drain electrodes as an etch mask. However, the source/drain electrodes may also be undesirably etched during etching of the doped amorphous silicon layer.
In order to reduce etching of the source/drain electrodes, a photoresist pattern that is used to form the source/drain electrodes may also be used as an etch mask to etch the doped amorphous layer. The photoresist pattern is then stripped. Unfortunately, however, the amorphous silicon layer may be damaged when stripping the hardened photoresist pattern. This may degrade the performance of the thin film transistors and liquid crystal displays.